The invention concerns a method for monitoring a chain pulley block with an electric actuator motor, which is connected at the drive side to a transmission across a sliding clutch. The invention also concerns a chain pulley block with an electric actuator motor that is connected at the drive side to a transmission across a sliding clutch.
From German Patent DE 199 27 847 C1 there is known a chain pulley block with an electric actuator motor, whose motor shaft is connected to a secondary transmission. The motor shaft is connected across a sliding clutch to an input shaft of the transmission. At the end of the transmission input shaft opposite the actuator motor there is arranged an electromagnetically activated disk brake.
Also, chain pulley blocks are generally familiar that have their brake arranged on the driven shaft of the actuator motor and thus before the sliding clutch.
In such chain pulley blocks, an overloading of the chain pulley block, a defective end switch, or a failure to release the brake due to a malfunction can not only result in an undesirable slippage of the sliding clutch, but also to thermal overload thereof. Depending on the design of the chain pulley block, this can lead to intense wear or disruption of the sliding clutch, or even a dropping of the load.
Furthermore, there is known from German Patent Application DE 38 38 058 A1 a device for monitoring a drive chain for interruption in the flow of force. The drive chain here has a positive force transmission between an electric motor and a load attachment point in the form of a cable drum of a cable pulley block. The cable drum is teamed up with an accessory brake, which is activated upon detecting a deviation in rotational speed between a first speed sensor assigned to the electric motor and a second speed sensor assigned to the cable drum. Thus, the accessory brake can prevent a load from being dropped.
This monitoring device does not provide for switching off the electric motor when the frictional connection is interrupted, since, when the flow of force is interrupted, it simply runs idle with no load. Here as well, the monitoring takes place by evaluating two speed signals from two speed sensors. This monitoring device does not identify a deviation in the speed of the electric motor from its rated duty in the sense of excessive or inadequate speed.